Monthly 1 send a mail in native HTML. January, with 3.4.6 all was ok. February, with 3.5.1, there was only the Mail-header, the body was empty, same appears march with 3.5.2.
I has uploaded the 2 files on dropbox:
thanks wolfgang
Something was wrong with the installation.
I deleted phplist and installed it new, and all was ok.
thanks for your help